Abstract

An emission band has been observed near 820 nm in a series of KTiOPO4 crystals grown by the flux technique. Photoluminescence spectra were obtained at room temperature using an excitation wavelength of 457 nm and a power density of 1.9 kW/cm2. When a crystal was held for 1 h in air at 1000 °C, the intensity of the emission increased by two orders of magnitude. Micro‐Raman spectra taken at the same location as the photoluminescence revealed that the high‐temperature anneal caused significant decomposition at the KTiOPO4 surface. Potassium, phosphorus, and oxygen evolved from the surface and left TiO2 (anatase). The increase in emission correlated with the amount of anatase created. This enhanced near‐infrared emission arises from Ti3+ ions which are formed by reduction in the TiO2 surface layer during the decomposition process. Since the 820‐nm emission is observed in as‐grown crystals, our data suggest that some reduced TiO2 (rutile or anatase) is formed in the bulk of KTiOPO4 crystals during growth.